Project Summary Primary and secondary pathogenic processes affecting glomerular podocytes contribute significantly to the burden of end-stage renal disease (ESRD). Despite significant evidence identifying the podocyte as the key glomerular cell target for injury, validated therapeutic targets are scarce and commercially available cell-specific therapy is lacking. Our long-term goal is to identify key regulatory pathways and therapeutic targets in the treatment of glomerular disease. Our work has identified the urinary serine protease plasminogen as a mediator of podocyte injury and a targetable biomarker that correlates with albuminuria and renal function. The overall objective of this application is to define the role of plasminogen as a ?second hit? mediator of podocyte injury and a potential therapeutic target in progressive glomerular disease. Our central hypothesis is that under normal conditions with an intact glomerular filtration barrier, podocytes are not exposed to plasminogen. In proteinuric disease, plasminogen enhances podocyte injury through urokinase type plasminogen activator as part of a second hit with plasminogenuria correlating with the risk of glomerular disease progression . The rationale for the proposed research is that characterizing the role of plasminogen in podocyte injury and glomerular disease progression could define it as a targetable biomarker in the treatment of proteinuric kidney disease. Our hypothesis will be tested by pursuing two specific aims: Aim 1 will define the role of plasminogen in podocyte injury and glomerular disease. We will define the mechanism by which plasminogen induces podocyte injury, test the role of podocyte plasminogen activator inhibitor 1 in glomerular disease progression and leverage the CureGN cohort to define the relationship between urinary plasminogen and human glomerular disease progression. In Aim 2 we will test plasminogen inhibition as a therapeutic strategy in proteinuric kidney disease using genetic models as well as novel pharmacologic compounds targeting plasminogen activation. Our innovative approach utilizes state of the art cell and molecular biology, biomarker analysis, imaging, systems biology and medicinal chemistry tools to define plasminogen as a mediator of glomerular disease progression. These contributions are significant because they are part of a continuum of research that is expected to advance understanding of glomerular disease progression and identify therapeutic targets and strategies to improve clinical outcomes.